The invention is concerned with an arrangement for switching data between any two of a plurality of ports, and a method for operating said arrangement.
A data transmission network serving a large number of terminal units requires switching nodes which can selectively transfer data arriving at any one of a plurality of lines attached to the node to any other line attached to the same node. The lines may be individual lines or trunks shared in multiplex mode for plural connections.
Data can be transferred through a network in circuit-switched mode, i.e. over a reserved connection, or in store-and-forward switched mode, i.e. in blocks from node to node with intermediate buffering of each block. An integrated network handling both kinds of traffic may be desirable for certain reasons.
For block-switching (packet-switching) several systems are known in the art which contain data processing units (processors). The switching arrangements known in the art have either a common storage and a common processing unit which are used for all attached lines (ports), or they comprise a plurality of processors cooperating with one, or a plurality of, storage units common to all processors.
The first (uniprocessor) type of system must be designed ab initio for the maximum traffic anticipated. This is incompatible with gradual incremental growth which is often desirable. Also, the processing unit is required to be very powerful so as to be able to control operation of the whole switching arrangement and scheduling of all switching transactions.
In known systems of the second (multiprocessor) kind, the modular structure is advantageous for incremental growth. However, many additional data transfers are necessary, partly to effectuate exchange of traffic between the processing units (if these units are available to all ports of the system on an arbitrary assignment schedule) and partly to exchange supervisory information (because all processing units must have complete information on current allocations of the common storage and compete with each other for storage accesses). These additional data transfers and the necessity for the processor modules to have complete information on storage allocations limit the number of such processor units which can be combined in a unified exchange system. As more and more processing units are added, there is a saturation effect; i.e. a maximum switching efficiency is reached which cannot be increased despite addition of more processing units. In turn this imposes limits-- in multiprocessor systems which have common storage separate from the processors, or in which an arbitrary assignment of processors to individual switching transactions is made-- on the data throughput capability which can be achieved and thereby may prevent economic and orderly fulfillment of future growth requirements.